Restriction Digests—Nature of Overhangs The unpaired single-stranded nucleotides left at DNA termini after certain restriction enzyme cuts are referred to as:
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ASticky ends
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BSingle strands
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CRestriction fragments
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DLigases
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EPolylinkers
Answer
Correct Answer: Sticky ends
Explanation
Introduction / Context:Restriction enzymes can generate either blunt ends or single-stranded overhangs. Overhangs provide complementarity that facilitates specific annealing and efficient ligation in recombinant DNA techniques.
Given Data / Assumptions:
- Some enzymes (EcoRI) produce 5' overhangs; others (KpnI) produce 3' overhangs.
- Overhangs enable base-pairing with compatible ends.
- Terminology distinguishes overhangs (“sticky ends”) from fully double-stranded “blunt ends.”
Concept / Approach:“Sticky ends” describes cohesive termini with unpaired nucleotides that can hydrogen-bond to complementary sequences. This property is exploited to directional-clone inserts into vectors cut with compatible enzymes.
Step-by-Step Solution:
Identify that the question refers to unpaired nucleotides at ends.Recall the standard term: sticky (cohesive) ends.Exclude unrelated terms (ligase is an enzyme; restriction fragments are the cut pieces regardless of end type).Verification / Alternative check:Cloning manuals define sticky ends as overhangs that anneal via base pairing prior to ligase sealing of the backbone.
Why Other Options Are Wrong:
- Single strands: too generic; does not denote cohesive ends specifically.
- Restriction fragments: includes blunt- and sticky-ended pieces.
- Ligases: enzymes that seal nicks; not DNA ends.
- Polylinkers: engineered multiple-cloning sites in vectors.
Common Pitfalls:Confusing overhang type (5' vs 3') with the general property “sticky.”
Final Answer:Sticky ends